Training Optimization and Performance of Single Cell Uplink System With Massive-Antennas Base Station

We study the performance of uplink transmission in single-cell wireless systems, where all the transmitters have single antennas and the base station has a large number of antennas. We consider both maximum ratio combining and zero-forcing receivers and both small- and large-scale fading channels. We also characterize the achievable total degrees of freedom (DoF) of such a system without assuming channel state information at the receiver. The system DoF turns out to be the same as that of a single-user multiple-input multiple-output system. However, when the number of users is the same as the number of receive antennas, linear receivers are not sufficient for achieving the maximum total DoF. The amount of energy savings that are possible through the increased number of base-station antennas or increased coherence interval are quantified. Furthermore, the training period and training energy allocation under the average and peak power constraints are optimized jointly to maximize the achievable sum spectral efficiency (SE). The improvement on achievable SE provided by the training duration and energy optimization is verified through multiple numerical simulations.